Cyclic process of fiber liberation



Dec. l, 1931. G A, R|CHTER 1,833Q975 CYCLIC PROCESS OF FIBER LIBERATIONFiled Sept.

Dec. 1, 1931. fa A mCHT'ER 1,833,975

CYCLIC PROCESS OF FIBER LIBERATION Filed sept. e, 192s 5 sheets-sheet sl, 1931. G. A. RICHTER CYCLIC PROCESS OF FIBER4 LIBERATION Dec.

5 Sheets-Sheet 4 Filed Sept. 6, 1925 Dec. l, 1931. G. A. RICHTER CYCLICPROCESS Of" FIBER LIBERATION Filed Sept. 6, 1925 5 Sheets-Sheet 5Patented Dec. 1, 1931 UNITED STATES FFHCE PATENT GEORGE A. RICHTER, OFBERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, 0F BERLIN'rNEWHAMPSHIRE, A CORPORATION OF MAINE cYcLIcrBocEss or FIBER. LIBERATI'ON.Application led lSeptember 6, 1923. Serial No. 661,240.

This invention has among. its objects to provide a process for theproduction of a high-grade cellulose pulp, the fibers of which are longand silky and capable of producin a strong paper when subjected to theusua processes of paper manufacture. The ob- I'ject of -the inventionfurther is to provide a process by which there is a greater yield ofpulp with less loss through screenings than heretofore possible; toproduce a pulp which is more easily bleached, so as to provide 'a finalproduct of high color; and to accomplish the results by a quick cook incontradistinction to those processes in which the pulp is subjected tolow temperature for a relatively long time.

Another object of the invention already stated is toA utilize thecombustible content of `the waste liquor for the generation of steam andpower, to recover the mineral or inorganic content of the waste liquorin the form of raw material which may be utilized in the formation ofthe cooking liquor, and to produce and recover alcohol from the wasteliquor by the fermentation of the sugars thereincontained resulting fromthe process of digestion.

A further object of the invention, broadly stated, is' to reduce thecost of pulp production, to eliminate waste as far as possible, andreduce the cost of maintenance of the acid system. In accomplishingthese results, it is possible to avoid the pollution of rivers andstreams by the discharge of the waste li uor thereinto, such as isordinarily practise in the manufacture of sulphite pulp so-called.Further objects of the invention are to provide certain improvements inthe method of fiber liberation and in the variousv instrumentalities orcombinations of instrumentalities which are employed in carrying .outthe process.

For the cooking of the wood and the liberation of the cellulose fiber, Iemploy an w acid cooking liquor which comprises a soluble sulphate, .asoluble -sulphite and free S()2 in the form of sulphurous acid. I havediscovered that when a cooking liquor of thisl character isemplpyed-namely, one having .v as, its components a soluble sulphate(from by tests 2% to 4%) and a definite fairly large propor- A tion ofcombined SO2 (from .2% to 2% which. is considerably greater than thatformed by metathesis of'sodium sulphate in sulphurous acid solution)together with free SO2V (4% to 7%)-that a pulp is produced, the fibersof which are relatively long and silky so that paper produced therefromis comparable in strength with kraftpaper. A solution such as referredto may be produced b using as the raw materials a solu-` ble sulp ate,oxalate or acetate or othersodium saltof a weak acid, and either asoluble sulphite, sodium carbonate or caustic soda, together withsulphur dioxide, which is bubbled through the aqueous solution`to roducethe cooking acid having the requisite percentage of free SO2. As asulphate I employ one having as its base only one of the 1. alkali oralkali earth metals such, for exam- 7 ple, as sodium, potassium,lithium, zinc,

magnesium, but not calcium or any other base which produces an insolublesulphate.

The combined S()2 is likewise in the form of i a soluble sulphite, usingfor this purpose any one of the above-mentioned bases.I The wood to betreated is placed in a digester of substantially the same character asthat ordinarily employed in the manufacture of sulphite pulp so-called,but preferably the digester is heated by indirect heating instead ofbythe injection of steam, in order that the cooking liquor may not bediluted by thecondensate of the steam. A quick cook is preferablyeffected, thetemperature of the digestercontents being raised' toapproximately from 275 to 300 F. and the cooking being continued forapproximately nine to twelve hours. The liquor is circulated externallyfrom the bottom of the digester to the top thereof and is passed througha heater wherein it is heated by steam coils or other suitable heatingsurface. After the cooking operation has been completed as ascertainemade in the usual way from time tov time, the digester is blown into ablow-pit, and the vapors and gases arising therefrom are passed througha condenser wherein the steam is condensed by direct contact with water,and the chilled gases, comprising SO2 -jected to the recovery processes,

passing from the condenser, are utilized in the acidification of cookingliquor.

The waste liquor which is separated from the pulp and which containssodium sulphate, a certain percentage of sodium sulphite, a combustibleorganic content and various sugars, is now so treated as to effect thefermentation of the sugars and the recovery of alcohol, the combustionof the combustible content, and the recovery of the mineral content inthe form of sodium sulphate and more or less sodium carbonate. Incarrying out these several operations, I effect certain economies inopera-tion by methods which will be explained in detail in thisspecification. The loss of sodium constituent in the cooking operationis made up by the addition, inthe production of the fresh liquor, of thenecessary sodium constituents, and the loss in SO2 is made up by gases`'produced by the combustion of sulphur-bearing materials. In fact,after the process is in operation practically the only raw materialswhich are needed/for making up losses are sulphur or .sulphur-bearingmaterial, and either sodium sulphate, sodium sulphite, sodium carbonate,caustic soda, or other soluble sodium salts ofa weak acid, or acombination thereof.

Preferably, before the waste liquor is subits aqueous content is reducedby evaporation, which it- Self may take place in two steps. That is tosay, the waste liquor may be evaporated to a certain degree ofconcentration prior to its being fermented, and the final stepof-evaporation may be accomplished after the fermentation and alcoholrecovery, but'prior to the delivery'of the waste liquor to the retort inwhich the mineral content is recovered and the combustible contentconsumed. On the accompanying drawings,

Figures la, 1b, 1 and 1d on Sheets 1, 2, 3 and 4 illustratediagrammatically and conventionally the various instrumentalities whichmay be utilized in ,carrying out my process, the said figuresconstituting an 'illustration of the entire systennwhen placed side byside in sequence.

Figure 2 represents a part of the system including the combined retortand bbiler furnace, a scrubbing and recovery tower, a dissolving tankfor receiving the eiiluent from the furnace, a scrubbing tower tank anda cooler.

The instrumentalities employed in the system are shown onlyconventionally and diagrammatically by the several figures of thedrawings.

On the drawings 1 is a digester of the proper dimensions for carrying onthe cooking operation. Atthe lower end of the digester I have indicatedconventionally a screen 2 and a conduit 3 for the Withdrawal ofthe-screened cooking liquor, which is pumped by pump 4 through anindirect ing conduit 3. At 7 I 'have indicated a b -pass so that theliquor may be continuous y circulated through the heater to maintain theefficiency thereof.' The valves8 and 9 may be used to regulate thepassage of the liquor through the by-pass and into the -digester so astopcontrol the rate of flow of liquor in the digester and thetemperature thereof. -In this way it is possible to circulate the liquorrapidly through the heater, raising it to the desired temperature, andtol draw olf such liquor therefrom as may be needed in bringing thecontents of the digester to and maintaining them at the desired cookingtemperature and pressure. After the cooking operation is completed, thecontents of the digester are blown through the blow pipe 10 to ablow-pit indicated at 11. The liberation of the digester contents in theblow-pits is accompanied by thel formation of steam or vapor and theliberation of SO2.A The vapors and gases are conducted from the blow-pitinto a direct condenser indicated as a whole at 12. This condenser maybe substantially like that illustrated in my pending application-SerialNo. 405,915, 1920, and it contains a mass of inert interliled onAugust25,

stitial material such as spiral bricks, rocks,

ture slightly less than the boiling point. The

cooled gases containing from 30% to 60% S02 are conducted from the topof the condenser tower by formation of t e cooking liA uor, as will beexplained. lThe heated coo in water delivered from the lower endiof t econdenser tower may be conducted by pipe' 14 to a storage Atank 16, fromwhich it is drawn for purposes to be subsequently explained.

From the blow/pit the pulp and the waste liquor are forced by a pump 17through a pipe 18 to what I may term for convenience an unwashed-pulpstorage tank 19. It is now necessary to separate the pulp from the wasteliquor and to wash the pulp so that it may be freed from the liquor andbe in a condition to be sent to the usual screens which are employed forrefining the pulp and removing the so-'called screeningsl therefrom,which consist of knots, specks, particles of brick, cement, etc. At 20and 21 I have pipe 15 and utilized in the,

indicated a series of pulp washers, arranged in two groups, one of whichfor convenience I may term the strong liquor washer and the other theweak liquor washer, the pulp 'passing continuously through both seriesof washers. These washingniachinesare preferably substantially like`those illustrated and described in the patent of Brown, Martinson,Moore & Parker, No. 1,421,664, dated July 4, 1922, although if desiredone may utilizethe ordinary rotary vacuum type of pulp and the wasteliquor are forced by pump 24 from the .tank 19 to a conduit 25.to thefirst of the group of washers indicated at 20, and the pulp which isdelivered from said series passes to the -second group of washersindicated at 2l. The washed pulp delivered from the second group isdelivered to a washed pulp tank 27, from which it may be drawn olf anddelivered to the usual screens (not shown) by a conduit 28. The

purpose of subjecting the pulp to the operation of two `groups ofwashing machines is so that I may employ the wash liquor which isrelatively weak in inorganic.chemicals from the group of washers 21 forone purpose and the strong wash liquor from the'other group for anotherpurpose which I will make clear, this making for a more efficientrecovery of the valuable constituents ofthe waste liquor withoutentailing a corresponding dilution of the liquor which is subsequentlyevaporated. A certain amount of water from group 21 passes to group v20.The strong washing liquor delivered from the series of washers 20 isdischarged into two tanks indicated at 29 and 30 by a conduit 31, havingvalved branches leading to the two tanks. The amount of liquor deliveredto each tank is controlled as may be desired. A certain amount of thewash liquor which contains also the original waste blow-pit liquor isutilized for sluicing the lblow-pit and removing any pulp which mayremain therein after the blowing operation has beenl completed.' Forthis purpose' there is an outlet pipe 32 leading from the tank 29 andprovided with a pump 33 by which the-liquor may be deliveredptothebloW-pit for the' sluicing operation and from which it passes back tothe conduit 18 to the storage tank 19. As the wasteliquor is acid, it isdesirable to neutralize this acidity by an alkali, and for `37, so thatit is cooled to this purpose I preferablyv utilizea caustic ,I

soda solution which is contained in a caustic storage tank 34 and fromwhich 1t 1s drawn as desired by an outlet pipe 35 leading to the g tank29. The proportionate amounts of the caustic delivered for admixturewith the liquor from thelirst series of washers'20 are such as tomake'the liquor therein slightly alkaline and to compensate for lossesin sodium sulphite occasioned in the cooking liquor during the processof digestion. The proportionate quantity of the liquor delivered fromthe series of washers 20 to theltank 29 is so regulated that asubstantially constant amount of liquor is circulated from the tank backthrough the blow-pit, the u nwashed pulp storage tank 19, tothe washers2() and thence to the tank 29, so that after the process y is inoperation the greater quantity of the liquor coming from the blow-pitand `delivered to the washer-s 20 is passed to the waste liquor storagetank 30, from which it is drawn for evaporation and concentration. Inelect, the tank 29 and the conduits last referred to comprise a by-passbetween the washers 20 and the tank 30 so that waste` blow-pit liquormay be circulated for the pur- A pose of cleaning the blow-pit andsupplying the necessary alkali for lneutralizing the acidity of thewaste liquor from the blow-pit. Of course, it will be understood thatwhereas I have shown but a single digester connected with the blow-pit,I may utilize a bank of digesters all discharging into the same blowpitor a series of blow-pits all connectedwith the same tank 29 with properyvalved connections for delivering the sluicing lliquor to thedseveralblow-pits if more than' one be use The tank 3() containsv substantiallyall'of the waste liquor which was delivered lfrom the blow-pit, togetherwith a small amount of alkaline liquor delivered from the "causticstorage tank 34, and this liquor is now treated for the production andrecovery of alcohol, and thereafter forthe recovery of 'its othervaluable constituents. Prior to these opera'- tions, however. it isdesirable that the liquor should be subjected to evaporation for theremoval of a portion ofthe aqueous content. For this purpose I haveillustrated conventionally at 36 a series of multiple effectevaporators, the details of construction of which it is unnecessary todescribe'. W'hile I` preferably employ multiple-effect evaporators, anyother form of evaporator for removing a part of the aqueous content ofthe liquor may be utilized..v From the last effect of themultiple-el'ect evaporators the liquor which has been concentrated tol'about 16 B., and which contains about- 25% solids, is passed through acooler indicated conventionally at a temperature suitable forfermentation. The liquor which enters the evaporators is either slightlyalka- `ranged in groups.

line or substantially neutral,and with ther removal of the Water becomesslightly acid dueto the decomposition of certain organic constituents ofthe liquor, so that the liquor delivered from the cooler 37 -is slightlyacid. This liquor, While it contains sugars, is not per se suitable forthe most efficient propaga tion and maintenance of yeast for thefermentation of the sugars, and it is therefore desirable to add to theliquorany suitable yeast nutrient. For this purpose I preferably employmolasses from sugar cane, such as ordinary black molasses, for which, onthe drawin s, there is indicated a tank at 38. From this tank themolasses may be drawn to a measuring box 39 by a valved p ipe 40, sothat a predetermined quantity of molasses may be measured out foradmixture with al given quantity of the Waste liquor. .Inasmuch as thefermentation requires some hours, I provide a plurality of fermentationtanks which are preferably ef relatively small size and ar- Thus theymay be arranged in six groups of two, vthree groups of four, four groupsof three, or the like, as most convenient. From the cooler 37 extends apipe line 41 having valved branches 42 lead lng therefrom for deliveryof the Waste liquor to the various tanks indicated at 43. Similarlythere is a pipe line 44 for the molasses and from it extend valvedbranches 45 to the several tanks 43. It has been determined that by theaddition of, say, 3% to 4% by weight of molasses to a given quantity ofwaste vtemperature of approximately 80 tov90 F., .and to the liquor inthese tanks is' added liquor of say 16 B., it is possible by theaddition of yeast taken from a yeast box 46, to cause the acclimationand` propagation of yeast cells inthe liquor for the fermentation of thesugars contained therein. In the present instance, the liquor issupplied from'the cooler to the first group of three tanks at a about3%'to 4% of molasses. A sufficient uantity of yeast is then added toeachvof t ese tanks and the liquor is permitted to rey main thereinuntil the yeast is propagated in sufficient quantity for thefermentation of the sugar. On certain occasions it may be desirable toadd a small quantity of nitrogenous material such as ammonium phosphateor ammonium chloride. While the fermentation is going on in the firstgroup of tanks, the waste liquor is next supplied to the second group ofthree tanks, to which molasses may be added, as is explained, togetherwith yeast. There is a valved outlet from each of the fermentation tanksconnected with a pipe line 47.by which the fermented liquor may bedecanted `to a tank therefor, indicated at ,48.v `I do notherein. claimspecifically the process of adding a small predeterminedl quantity' of anutritive element, (together with yeast if required), to successivebatches of the yeast liquor, as that process, per se, is

that consistency at which, it contains about 50% solids. The vaporcontaining the alcohol is conducte-d from the evaporator through aconduit 61 to a condenser 62, with which is connected' a vacuum pump63,. The condensed Water and alcohol are delivered by a conduit 64 to astorage tank 65. The aqueous alcoholic solution has approximately a 2%3%content of alcohol, and by fractional distillation the alcohol issubsequently removed from the Water' and recovered, being subjected ifdesired to such refining processes as may be needed. The concentratedWaste .liquor delivered from the evaporator 60 is conducted by a pipe 66to a storage tank 6 7, from which it is Withdrawn for the combustion ofthe combustible content and the re covery of the basic inorganicchemicals, such as sodium sulphate and sodium-carbonate. I do not hereinclaim specifically that process o f treating fermented Waste liquorwhich consists in` subjecting it to evaporation for the concentrationthereof and the Simultaneols removal of alcohol and a part of itscontained water, and the further'sepa-ration and the qualitativeevaporation of the Water and alcohol by fractional distillation.l TheWaste liquor which has been subjected to concentration and fermentation,and from which the fermentable sugar has been fermented and removed asalcohol, contains a large quantity of solid matter, comprising.combustible 1 sulphur organic substances, sodium sulphate. and somesodium sulphite. :In drawing the fermented liquor from the 'fermentationtanks, the yeast is permitted to Lsettle in the' bottom of the tanks andto remain therein.

' Consequently there remains in each tank sufficient yeast for the nextbatch of Waste liquor, to which is added a given quantity ofmolasses,together with fresh .yeast if ythe latter is required. l'

The concentrated liquor intank 67 after the removal of the alcohol isnow subjected both to heat and pressure vto generate an exv plosiveforce therein, substantially as .described in Patent No. 1,326,414 toMoore & Quinn, dated December 30, 1919. To this end v the concentratedliquor is drawn from the tank 67 by a pump 68 through a pipe 69, and itis circulated through a circulating system comprising the pipe r70 whichiseonnected'to the pipe 69, the latter'being provided with a checkvalvevindicated at 71. The liquor in passing under pressure through thecirculating system isheated to a temperature above the boiling point bya heater 72 and" is de'- l i or series of pipes 7 3, terminating innozzles extending into a combined boiler furnace and retort indicated asa whole at 74. In the present instance it is desired that the sodiumcompounds recovered from the furnace should contain sodium sulphate andsodium carbonate. lf this recovery takes place in an oxidizingatmosphere, there is no dificulty in recovering the desired salts. Onemay, however, operate the furnace as most convenient, taking precautionsto eliminato the presence of sodium sulphide prior to the point in thesystem where the alkaline liquors come in contact with the strongsulphur dioxide gases of the acid system. One may employ a. furnace as-shown in Fig. 2. In this case what may be termed the combustion chamberof the furnace is provided with a floor 75 which preferably extendsrearwardly and downwardly from the front of the furnace into which project the nozzles 76 for the emission of the waste liquor. The floor atthe rear wall of the furnace is provided with spouts 77 from which themolten eiiiuent escapes from the furnace. Opposite the nozzles andprojecting downwardly from the lues 78, there is a bridge wall 79 whichterminates a short distance above the floor 75 so that the gaseousproducts of combustion will pass downwardly thereunder before passingthrough the flues and upwardly through the stack 80. Notwithstandingthat an explosive force is generated in the waste liquor and the wasteliquor is disrupted, leaving the nozzles so thatit is more or lessconsumed in transit t before reaching the floorof the furnace, yet

there are'drops of the Waste liquor which form on the nozzle and fall tothe floor of the furnace. By inclining the floor rearwardly, such wasteliquor as is dropped upon the floor must fiow downwardly through thehottest part of the combustion chamber and be subjected to an oxidizingatmosphere, as in the present instance. To supply an oxidizingatmosphere the sides of the furnace at suitable points may be providedwith air inlets indicated at 81, certain of these inlets being locatedin the rear and others in front of the bridge wall 79. By provision ofthe bridge wall, the gaseous products of combustion including CO2 arebrought into contact with the smelt to insure the conversion to carbon-4. ate and sulphate of any sodium sulphide that may be formed in theportion of the furnace where there is, because of the nature of things,a reducing atmosphere. A fan 82 connected with the stack assists inmaintaining a reduced pressure in the stack and back through the furnaceand also delivers the escaping products of combustion under pressure toa scrubbing tower` 83. This scrubbing tower consists of an elongatedvertical shell of wood or other suitable material containing a mass ofspiral brick or other inert interstitial material supported by aperforated diaphragm .spaced from the bottom of the tower. The

4SO2 as may be formed in thefurnace, are

caused to pass upwardly through the tortuous passageways ai'orded by theinterstitial material and meet the downflowing stream of the liquor(derived from a source to be explained) which is supplied to the top ofthe tower, as a result of whichI am able to recover many valuableconstituents which otherwise would be wasted in the atmosphere, and allwithout the use of an electrical `precipitator or other expensiverecovery apparatus. In fact, by the provision of the scrubbing towerconstructed as described, I am able to recover sulphur in the form ofSO2 which is not recoverable by the employment of a Cottrell or otherelectric precipitato-r. The waste gases, (consisting substantially ofnitrogen and carbon dioxide), emerging from the top of the tower aredelivered to the atmosphere through a vent 84. The liquor which emergesfrom the bottom of the tower` is conducted by a conduit 85 to what Ihave termed a dissolving tank 86 for the purpose to be explained. 'Llhemolten efliuent from the furnace consisting of a soluble sulphate and a`soluble carbonate are delivered from the spouts 77 to the dissolvingtank 86 and are dissolved in the liquor supplied to that tank fromthescrubbing tower. A part of this liquor is circulated back to thescrubbing tower by a pump 87 and pipe 88, so that itl will be seen thatthere is substantiall continuous circulation of liquor fromthe'dissolving tank to the scrubbing tower andback again. The freshliquor which is supplied to the dissolving tank isdrawn from the seriesof weak liquor washers indicated at 21' and is conducted therefrom tothe dissolving tank by a pipe 89. Inasmuch as a part of the liquor fromthe dissolving tank 86 is circulated through the scrubbing tower and asthere is a constant fresh accretion of liquor from the washing machine21, it is desirable to provide a storage tank for the surplus priortoits subsequent use, and for this purpose I employ a storage tank 90,to which liquor is pumpe from the dissolving tank -86 by -a pump 91through a cooler 92 and a lter 192. By passing this liquor through thefilter, I am able to remove any adventitious solid matter that may becontained in the liquor.

As thus far explained, it is quite clear that the only fresh water whichhas been added to the system is that which was supplied for the directcondensation of the moisture and the cooling of the gases in thecondenser tower connected with the blow-pit, and that which was added informing the caustic solution introduced into the tank 29 prior to thefirst washing of the pulp, all of the li uor which is utilized forscrubbing, for the orming of 'the fresh solution, and the like, beingprovided by the wash liquor and the added water previously referred to,but an addition-al supply of hot water may be provided by pipe 129 tothe hot water storage tank 22. The efliuent from the furnace, whendissolved in the wash liquor lin the dissolving tank, to which vthe weakliquor from the second series of washing machines wasdelivered afterbeing filtered and delivered to the stora e tank 490, is` in conditionto be acidiiied by 02. This may be accomplished in any suitable way, bybubbling SO2 gas through the liquor or causing such liquor and the SO2to pass in countercurrent flow through a suitable tower or series oftowers containing inert interstitial material. Preferably, however, itis desir- .able for increasing the strength of the liquor in SO2 s o asto provide cooking liquor having a relatively high free SO2 content, ItoeHect the acidification of the liquor by a series of steps which may becarried on continuously. It will be understood, however, thatindescribing the preferred process for acidifying the liquor the presentinvention is not limited to the employment thereof, as any suitablemethod of acidifying the liquor to produce one havin a predeterminedpercentage of combined O2 and a predetermined percentage of free SO2 maybe utilized. The liquor containing the dissolved eiiiuent from thecombined boiler furnace and retort comprises, as has already beenstated, a soluble sulphate,-e. g., sodium sulphate-and sodium carbonate.The sodium carbonate by reaction with SO2 is formed into sodiumsulphite, sufficient caustic soda having been supplied to theoriginal'waste liquor to provide for a suiiicient proportion of thecarbonate to be formed into sulphite as may be desired. In

the case as previously stated, I produce a liquor having from 0.2% to 2%combined SO2 as sodium sul hite, approximately 2% to 4% sodium sulp ate,and from 4% to 7% free SO2. The acid system so-called by which theliquor is acidiiied may comprise the follow-ing instrumentalities:Towers .indicated at 94, 95 are provided with inert interstitialmaterial, and the liquor from the tank 90 is forced by a pump 96 through.pipe 97 to the top of t e tower 94. The liquor from the vlower end ofthe tower is conducted by a pipe 98 to a storage tank 99. The liquorwhich leaves the tower 94, in order to distinguish it, may be termedweak acid liquor, since in leaving the tower it contains only from 0.2%to 0.4%free SO2, from 0.21% to 2% combined SO2, and from 2% to 4%Na2SO4. Thisliquor is now ready to be delivered to what may be termedthe raw acid liquor system which comprises towers indicated at 100 and101, and

consequently is pumped by pump 102 through pipe 103 to the top of thetower 100. These towers, like those at 94 and 95, are provided with amass of linert interstitial material such as spiral brick, rock and thelike, and after the liquor is passed downwardly through the tower 100,it is forced by pump 103 to the top of the adjacent tower 101. In v llet or vent pipe 106. The weak acid liquor,

after being paged in series through the two towers 100 and 101, emergesfromthe latter as what may be termed for convenience a raw acid liquor,and is conducted from the tower 101 to a storage tank 107 through thepipe 108. vThis liquor as it reaches the storage tank 107 contains from2% to 2.5% free SO2 in addition to the combined SO2 and the sodiumsulphate originally in the weak liquor. From this last-mentioned storagetank 107 the liquor may be drawn for further strengthening by theaddition of sulphurous aci n will be rewind' that during each blow ofdigester contents there emerges from th blow-pit condenser 12- a largequantity or volume of cooled gases containing approxi-' mately 50%-60%SO2. Consequently for the recovery of these gases it is desirable to usea portion of the'liquor which is undergoing acidiflcation. The cooledgases are delivered from the blow-pit condenser at intervals orintermittently4 so that when this is occurring it is necessary to supplyfor the time being a quantity of ,liquori for the recovery of the SO2.This is accomplished by 4 drawing the raw acid liquor contained inthestorage tank 107. Hence, leading from the last-mentioned tank there is avalved conduit includinga pump 109, for delivering the raw acid liquorto the top of the tower 95; and the conduit 15 for the gases from thecondenser 12 is connected to the lower end of the last-mentioned towerso that when theliquor passes downwardly through the tower it-meets astrong acid gas by which its free SO2 content is materially increasedtoa point where it contains from say 2.7% to 3% yfree SO2. From the lowerend of this tower the fortified liquor is conducted by pipe 110 back tothe storage tank 107. Thus thepipe 180,

the tower 95 and pipe 110 afford a circulating system for circulatingthe raw acid liquor through the tower 95 for the absorption and recoveryof SO2 delivered from the condenser during al blow of the digester. It`may be noted that the gas, after passing through tower 95, is conductedby pipe to the lower end of tower 94. A vacuum pump 196 is connected tothe vent pipe 197 from tower A94. Even with the addition' of free SOLlto the liquor in storage tank 107, it is desirable ordinarily toincrease its strength 1n sulphurous acid, and for this purpose Ipreferably employ the relief gas discharged from the digester during thecooking operation. The relief gas pipe 111 leading from the top of thedigester conducts the gas through a cooler 112 and thence to the firstof a series of towers indicatedv at 113,' 114, 115 and 116. These towersmay be substantially as illustrated and described in my applicationSerial No. 503,- 8,46, filed September 28, 1921, and I do not hereinspecifically make claim thereto. It is suiiicien-t to say that for thepresent purposes each of 4these towers contains inert interl stitialmaterial tlibugh" which gas and the liquor may pass in series and incountercurrent flow. Thus the gas conduit 111 conducts relief gas to thelower end of tower 113 whence it passes in series through towers 1 14,115 and 116, and the tail gas which contains about 16% SOzis conductedby a pipe 117 from tower 116 to the buiner gas conduit 104, so that itmay be passed with the burner gases through the series of towers 101 and100. The raw acid liquor is drawn from the storage tank 107 .anddelivered first Vto the top ofl tower 116., and passing in seriesthrough .the towers, in ceuntercurrent flow to t.the gas, is finallydelivered to a conduit'118 to a large finished acid storage tank 119,whence i-t is drawn by pump 120 and valved pipe 121 asmay be desired forthe cooking of chips in the digester 1. The finished acid liquor asdelivered to the final storage tank 119 new contains the desiredproportion of (say, 4% to 7%) free SO2, combined SO2 (say, 0.2% to 2%)in the form of sodiuml sulphite, and

(say, 2% to 4%) sodium sulphate, for it will be recalled that the sodiumcarbonate delivered as a part of the euent from the furnaces has beenacted upon by SO2 with the consequent formation of sodium sulphite.

The water which is employed for cooling the gases and condensing thevapors, in the blow-pit condenser, notwithstanding that it is deliveredat a relatively high temperature from the condenser, contains a certainamount of SO2 which ma be recovered. 'Il-his I accomplish by passlngsuch swater, while heated, through an expelling tower 122, to which itis passed by pump 123 through pipe '124, andfrom which it passes throughpipe 125. to the hot water storage tank 22 hereinbefore referred to..rIhev tower 122 contains a mass of inert interstitial material, e. g.,spiral brick. Air is blown by a fanvor pump 126 through an inlet pipe127 to the lower end of the tower, and in passing upwardly in contactWith the trickling streams of water sweeps and removes therefromsubstantially all of its contained SO., and delivers the same through aconduit 12 to the stack 80 of the boiler furnace for recovery in theyscrubbing tower 83.

It will be understood by those skilled in the art that whereas -I havedescribed certain V preferred arrangements and combinations of thevarious instrumentalities, `nevertheless many changesmay be made thereofwithout departing from the spirit and scope of the 1nvention as setforth in the claims. Because -of the nature and small size of thedrawings it is impossible to illustrate the various instrumehtalities intheir exact relationship or at their different levels or in theirrelative proportions. Moreover, .various ley-passes, fittings and valveswhich are vused in the actual. construction of the entire system areomitted from the drawings in the interests of clarity. In Letters PatentNo. 1,427,125, granted on the 29th of August, 1922, I have described aprocess of fiber liberationin which the cooking liquor comprisesessentially an acid solution of a soluble sulphate, and I have pointedout that therewere, at times,small adventitious quantities of solublesulphite accidentally produced in the recovery of the sulphate from thewaste liquor. I have sinceA discovered, however, that by providingamaterial and appreciable deiinite quantity of soluble sulphite in thecook'- ing liquor, I am able to produce a pulp of when the cookingliquor contains only a soluble sulphate or a soluble sulphate with anegligible portion of sodium sulphi'te.. Consequently in accordance withthe presentinvention I add to the liquor to be used in 'c'ooking adefinite quantity of either a soluble sulphite or a salt which in theprocess of'recovery and` acidification by reactioirpproducesl a solublesulphite in sufficient predeterminedl quantities. In describing theapparatus .which is illustrated upon the drawings, I

have called attention to the employment of a caustic soda storage tank34 from which lcaustic soda is added to the waste liquor, to

the end that in the loxidation furnace the caustic soda may be recoveredas sodium car bonate and later converted to sodium sulph'ite by reactionwith SO2, but it is quite evident that instead of adding caustic soda atthe point indicated, sodium carbonatemight be added to the contents ofthe dis solving tank 86 for admixture with the solution produced by theaddition of the molten effluent of the liquor, or I` may add to thefinished acid liquor a certain definite propor-l tion of previouslyformed sodium sulphite. These all produce equivalent results, and Ishould not regard the adoption in lieu of the others as a departure fromthe spirit and scope of the present invention.

Although I have previously adverted to the fact, nevertheless I desireonce more to call .attention thereto, that in the recovery andutilization of the waste liquor, which includes the evaporation of theaqueous content, the formation and recovery of alcohol,

h herein set forth,

and the lrecovery of the inorganic content, only such Water as isemployedin making the fresh liquor by addition of the recovered sodathereto is that which is used in condensing and cooling the gas'es andvapors from the blow-pit, omitting from condensation the IWater which isused'in forming the caustic sodasolution contained in the tank 34,A andconsequently the Whole process is highly economical, although additionalWater may be drawn from a suitable source if desired. The acid-making,system is i easily and cheaply maintained, as there are no insolublesulphates or other waste products formed which require removal from timeto time. The

vonly Waste resulting from the entire system comprises those Waste ortail gases from the combined boiler furnace and retort and from thetower 100, which are indeed negligible, since these gases comprisesubstantially only nitrogen and CO2. The combustion of the combustiblecontent of the Waste liquor furnishes heat and power for operating thevarious pumpsand a sufficient excess of steam or power is provided forheating the digester contents and in utilization in other parts of theplant. As a result of the invention as l I not only produce a fine.,high-grade pulp which is easily bleached and which consists of long andsilky `fibers, but I also effect marked economies in the operation ofthe entire apparatus, in addition to savingliquon these conditionspracticable recovery of chemicals,

ing and recovering valuable products which would otherwise be wasted.

l have. herein described. the smelting and boiler furnace as providedwith an oxidizing atmosphere for the recovery of sodav in the form ofsodium carbonate and sodium sulphate, but it should be' understood thatsince the furnace-operating conditions bear a direct relationship uponthe final ratio of combined S()2 and sodium sulphate in the'cookmay bechanged according to any given circumstances. As herenbefore described,the conditionsare preferably such as to avoid the formation of sodiumsulphide, but under conditions in `which the sulphide could Withouttrouble be converted .to carbonate, the atmospheric conditions in theretort could be changed. TheV process as herein outlined provides for aand a cycllc operation, in addition to the production of pulp of thecharacter hereinbefore de' scribed. This follows, from the use of bothsoluble sulphate and soluble sulphite in the cooking liquor.

What I claim is':-

1. A process of'iber liberation, which comprises digesting cellulosicmaterial in a sulphurouslacid solution comprising 0.2% to 2%'.combnedSO2 as a soluble sulphite and 2% to 4% of a soluble sulphate.

2 .jA process of'fiber liberati-on, which comprises digesting cellulosicmaterial ina sul'- which comprises cooking in a digester ravv`cellulosic material in a sulphurous acid solu tion of a sodium salt,condensing the vapors from the hot Waste liquor resulting from suchsmelting and recovering in such Water sodium salts of such Waste liquor,and acidifying the resulting solution for use in digesting fresh rawmaterial.

4. A process such as herein described,

which comprises cooking in a digester raw cellulosic material in asulphurous acid solution of a sodium salt, condensing the vapors fromthe hot Waste liquor resulting from such digestion by direct contactwith Water, Washing the pulp with the resulting hot Water, smelting andrecovering in the Water from such Washing sodium saltsl from said Wasteliquor, and acidulating said Water containing said salts for digestingraw cellulosic material.

v5. A process such as herein described, which comprises cooking in adigester ravv cellulosic.. material in a sulphurous acid solution of asodium salt, condensing the vapors from the hot Waste liquor resultingfrom such digestion by direct contact with Water,`

Washing the pulp with the resulting hot Water, smelting and recoveringin the 'Water from such Washing sodium salts from said Waste liquor,recovering in said Water soluble -salts from the products of combustionisaid smelting operation, and'acidulating such Water for use' indigesting raw cellulosic material.

6. A process such as herein e described, which comprises cooking in adigester raw cellulosic material in a sulphurous acid solution of asodium salt, condensing the vapors from the hot 'Waste liquor resultingfrom such digestion by direct contact with Water, Washwhich comprises'cooking in a. digester raw cellulosic materiall in a sul hurous acidsolution of a sodium salt, con ensing the vapors from the hot wasteliquor resulting from such digestion by direct contact with water,removing free SO2 from such water, washing the pulp with such Water,recovering free SO2 from the waste cooking liquor, concentratingdigestion by direct contact Wlth Water,

' and burning the combustible content of the lution of a sodium salt,condensing the va.

pors from the hot Waste liquor resulting from such digestion by directcontact with q Water, smelting and recovering'in such water sodium saltsof such waste liquor, acidifying the resulting solution for useindigesting fresh raw material, and supplying to said solution suchsodium compounds an sulphurous acid as required to bring the same toproper strength as acid cooking liquor.

9. A process as herein described, comprising cooking raw cellulosicmaterial in a sulphurous acid solution of a soluble sulphur compound ofthe alkali or alkali earth groups, during which the cooking liquor isheated by heating surfaces and not by direct steam, condensing thevapors from the resulting Waste cooking liquor by direct contact withwater, recovering SO2 from said Waste cooking liquor, washing the pulpin said condensing Water, smelting and recovering in said water theinorganic content of said cooking liquor, and acidulating such waterWithA said recovered SO2. V

10. A process as herein described, comprising cooking raw cellulosicmaterial in a solution of a soluble sulphur compound of the alkali oralkali earth groups, during which the cooking liquor is heated byheatingsurfaces and not b direct steam, evaporating and concentratingthe waste cooking liquor, subjecting such concentrated liquor tofermentation for the formation and recovery of alcohol, burning thecombustible content, and smeltin and recovering the inorganic content oft e remaining waste liquor. l

11. A process as herein described, comprising burning the combustiblecontent and smelting the inorganic content of a waste cooking liquorresulting :from the digestion of raw cellulosic material containingcompounds of the alkali or alkali earth groups, recovering said smeltedinorganic compounds in an aqueous solution, conducting the products ofAcombustion `through a conned mass of inert interstitial material, andcirculating said solution through said inert material in-contact withsaid products of combustion for the absorption and recovery of thesoluble products thereof.

12. A process of ber liberation, which comprises digesting cellulosicmaterial in an acid solution containing substantial amounts of both asulphate and a sulphite of a metal of the alkalimetal group, the amountof said sulphite being considerably more than that formed by metathesisof the sulphate in sulphurous acid solution.

13. A process of ber liberation, which comprises digesting cellulosicmaterial in. a sulphurous acid solution containing substantial amountsof both sodium sulphate and 'sodium sulphite, thev amount of saidsulphite being considerably more than that formed by metathesis of thesulphate in sulphurous acid solution. l v

14. A process of ber liberation, .which comprises digesting cellulosicmaterial in a sulphurous acid solution containing a substantial amountof a soluble sulphate and d at least 0.2% of a soluble sul hite.

15. A process of ber li ration, which comprises digesting cellulosicmaterial in a sulphurous acid solution containing a substantial amountof sodium sulphate and at least 0.2% of sodium sulphite.

16. A process of aber liberation, which' comprises digesting cellulosicmaterial in a sulphurous vacid solution containing at least 2% of asoluble sulphate and at least 0.2% of a soluble sulphite.

17. A process of ber liberation, which 'comprises digesting cellulosicmaterial in a sulphurous acid solution containing at least 2% of sodiumsulphate and at least 0.2% of sodium sulphite.

In testimony whereof I have aiiixed my signature.

GEORGE A. RICHTER.

i loo

